Been working recently on an upload feed for magento – didn’t like the system at all at first but it sort of grows on you.
Had to map all the feeds from the main feed to the equivalent fields in Magento which was fun but i just parsed the data in SQL and generated a new format file. Interesting challenges here included getting the categories mapped correctly – definately need to set these up first before you try to do an import since any unmatched appear at store level – which is a pain when 400 items are there but easily fixed by mapping the xml file to the correct category id.
One issue was the feed upload kept stalling – but since it’s an upsert – this was fixed by reducing the file sizes.